Title:
Cretaceous Gross Spitzkoppe and Klein Spitzkoppe stocks in Namibia: Topaz-bearing A-type granites related to continental rifting and mantle plume
Publication Year:
2007
Abstract:
The anorogenic Damaraland intrusive complexes in Namibia belong to the bimodal Paraná–Etendeka Large Igneous Province and comprise mafic, silicic and alkaline plutonic and volcanic rocks that were emplaced into the Neoproterozoic Damara orogenic belt at 124 to 137 Ma. The magmatism was related to the Tristan mantle plume and continental rifting that led to separation of South America from Africa. Silicic plutonic rocks are found in the Gross Spitzkoppe, Klein Spitzkoppe, Erongo, Brandberg, Messum, Cape Cross, and Paresis complexes. The Gross Spitzkoppe and Klein Spitzkoppe stocks consist of texturally distinct types of topaz-bearing biotite (siderophyllite–annite) granites with columbite, zircon, magnetite, and monazite as typical heavy accessory minerals. A bimodal magmatic association is indicated by synplutonic mafic dikes and magmatic mafic inclusions. The stocks have rims of layered aplite–pegmatite stockscheiders against the country rocks. Miarolitic cavities and pegmatite-lined druses with gem-quality topaz and beryl indicate vapor saturation, and hydrothermal activity has locally produced wolframite-bearing greisen. The Spitzkoppe granites are highly evolved, marginally peraluminous (A/CNK 0.95 to 1.09) and characterized by high SiO2 (74.4 to 78.6 wt.%), Na2O + K2O (7.6 to 8.8 wt.%, with K2O prevailing over Na2O), F, Rb, and Ga, as well as low MgO, Ba, and Sr. The small but clear differences in REE patterns [(La/Yb)N in Gross Spitzkoppe 2.5 to 7.7 with mean at 4.4, in Klein Spitzkoppe 0.6 to 1.6 with mean at 0.9, more pronounced negative (Eu/Eu⁎)N anomaly in Klein Spitzkoppe] show that the granites of the Klein Spitzkoppe stock are slightly more evolved than those of the Gross Spitzkoppe stock. Overall, the granites exhibit A-type and within plate characteristics. Keywords: A-type granite, Rifting, Mantle plume, Petrogenesis, Geochemistry.
Publication Title:
Lithos
Volume:
97
Issue:
1-2
Pages:
174-192
Item Type:
Journal Article
Language:
en

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